If Rasulullah (sallallahu ‘alaihi wasallam) received divine revelation whilst mounted upon a camel, the camel would be forced to sit due to the weight of the wahi. Hazrat Zaid bin Thaabit (radhiyallahu ‘anhu) narrates, “On one occasion, the blessed thigh of Rasulullah (sallallahu ‘alaihi wasallam) was on my thigh when he started receiving divine revelation. His thigh became so heavy that I was afraid of my thigh being crushed.”
Thereafter, Hazrat Jibraa’eel (‘alaihis salaam) appeared before him giving him glad tidings of Allah Ta‘ala choosing him as His messenger until Rasulullah (sallallahu ‘alaihi wasallam) felt at ease. He then bade him to recite. Rasulullah (sallallahu ‘alaihi wasallam) asked, “How must I recite?” Hazrat Jibraa’eel (‘alaihis salaam) replied, “Read in the name of your Rabb Who created….” up to the verse “that which he knew not.” Rasulullah (sallallahu ‘alaihi wasallam) accepted the message of Allah and returned. Every tree and stone he passed while proceeding to his home greeted him with “Assalaamu‘alaika Yaa Rasulallah!” This is how Rasulullah (sallallahu ‘alaihi wasallam) returned home in happiness and with the firm conviction that Allah Ta‘ala had conferred upon him a magnificent bounty – prophethood.
(Extracted from Seeratul Mustafa 1/136-137)